Filament spool



FIG. 1 is a top front perspective view of a fourth embodiment thereof;

FIG. 2 is a top view thereof, the bottom of the fourth embodiment being unclaimed;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a left side view thereof; and,

FIG. 6 is a right side view thereof.

The broken lines in the drawings depict environmental subject matter only and form no part of the claimed design. 

The ornamental design for a filament spool, as shown and described. 